(1) Field of the Invention
This invention relates to containers for goods that are cooled by releasing cryogenic fluids thereinto, and more particularly to refrigeration control systems for such containers.
(2) Description of the Prior Art
Containers for shipping and storing fresh produce and frozen goods were cooled by the release of cryogenic fluids before my invention. In some cases, this "cryogenic cooling" supplemented mechanical/compressor-type cooling, while other systems were devised that used "cryogenic cooling" alone.
Before filing this application a search was made in the U.S. Patent and Trademark Office. That search revealed the following U.S. patents:
______________________________________ JOHNSON ET AL 2,479,840 ROSEBAUGH 2,479,867 DIXON 3,269,133 KANE ET AL 3,287,925 SNELLING 3,385,073 WILLIAMS 4,060,400 ______________________________________
These patents are deemed pertinent because the applicant believes the Examiner would regard anything revealed by the search to be pertinent to the examination of this application.
Although the refrigeration systems for prior art containers functioned satisfactorily under some conditions, certain inefficiencies were inherent in their design. Boil off gases result from heat transfer into the tank or bottle holding the cryogenic fluid coolant. Greater amounts of boil off gas are produced with tanks mounted outside refrigeration compartments. These designs usually vented the boil off gases outside continuously. This was extremely wasteful, inasmuch as this extremely cold gas could be used to cool the container.
Other prior art systems continuously vented the boil off gases into the compartment. This design sometimes produced too much cooling of the container.
The power requirements of the prior art refrigeration systems presented another problem. Most required repeated recharging of batteries or connections to external power sources during storage or shipment. These power problems are exacerbated when containers are used in holds of ships where external power sources are inconvenient or unavailable.